Liquid level control devices have been employed to control the level of water in a tank or the like, between predetermined levels. Furthermore, glass gauges or water glasses have been utilized for mounting exteriorally of the tank so as to visually observe the level of liquid within the tank.
One example of an earlier liquid level control device of interest is that found in U.S. Pat. No. 1,859,009, wherein a column cylinder of seamless steel houses two open water-filled floats of dissimilar weight which are connected with a whistle in such a manner that raising and lowering of the water level beyond predetermined limits permits the operation of the whistle. The cylinder has threaded and welded connections for attachment to the boiler and connection with a water glass.
Another prior alternative is disclosed in U.S. Pat. No. 4,186,419, which teaches apparatus for monitoring and controlling the liquid level in a storage tank by placing at least two magnetically operated switches at different levels in the tank and causing a magnet containing float to move in response to the liquid level to activate the switches. A relay operates upon activation of the higher of the switches to start electrical current flowing to operate a discharge pump thereby controlling the liquid level in the tank.
U.S. Pat. No. 3,437,771 relates to a float assembly constructed to include two relatively movable float elements, one of which is captive relative to the other, and in which the captive one is provided with magnetic means for operating or affecting magnetic sensing devices or switches.
Furthermore, U.S. Pat. No. 4,480,469 shows a device which is inserted in a tank and which device includes a float guided on a upright magnetically transparent tube which houses the relay switches, and where at least one of the switches is mechanically adjustable by use of a set screw for elevation within the tube.
Moreover, U.S. Pat. No. 3,419,695 teaches the use of a magnet and magnetic material such as a metallic ring, each mounted on a shaft within the tank, wherein the magnetic material attracts and retains the magnet in the event that the liquid carries the magnet into the vacinity of the magnetic material and prevents the magnet and float from falling under small or temporary liquid displacements to falsely operate the switch.
Finally, pivotally actuated float mechanisms have been used to control the level of water in a tank or the like.
Such liquid level control devices often fail to perform after usage due to a build up of mineral scale or deposits such as calcium or the like precipating from the liquid onto the moving parts of the control device, which inhibits the movement of the float mechanism. Such scale deposits may quickly form even after regularly cleaning the control device, depending on the condition of the liquid. Furthermore, one is not aware of the build up of such scale until the liquid level control device fails to perform as such device has been placed within the tank and therefore not visually observable.